[tip: x86/sev] x86/sev: Create snp_prepare()

[tip-bot2 for Tycho Andersen (AMD)]

The following commit has been merged into the x86/sev branch of tip:

Commit-ID:     ca2ca373ec854d203c74e6ac1c4e08a70e8d2509
Gitweb:        https://git.kernel.org/tip/ca2ca373ec854d203c74e6ac1c4e08a70e8d2509
Author:        Tycho Andersen (AMD) <tycho@xxxxxxxxxx>
AuthorDate:    Thu, 26 Mar 2026 10:11:05 -06:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Sat, 28 Mar 2026 22:16:03 +01:00

x86/sev: Create snp_prepare()

In preparation for delayed SNP initialization, create a function snp_prepare()
that does the necessary architecture setup.  Export this function for the ccp
module to allow it to do the setup as necessary.

Introduce a cpu_read_lock/unlock() wrapper around the MFDM and SNP enable.
While CPU hotplug is not supported, this makes sure that the bit setting
happens on the same set of CPUs in both cases.

This improvement was suggested by Sashiko:

  https://sashiko.dev/#/patchset/20260324161301.1353976-1-tycho%40kernel.org

Also move {mfd,snp}_enable() out of the __init section, since these will be
called later.

Signed-off-by: Tycho Andersen (AMD) <tycho@xxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Link: https://patch.msgid.link/20260326161110.1764303-3-tycho@xxxxxxxxxx
---
 arch/x86/include/asm/sev.h |  2 ++-
 arch/x86/virt/svm/sev.c    | 49 ++++++++++++++++++++++---------------
 2 files changed, 32 insertions(+), 19 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 0e6c094..2140e26 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -661,6 +661,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int pages)
 {
 	__snp_leak_pages(pfn, pages, true);
 }
+void snp_prepare(void);
 #else
 static inline bool snp_probe_rmptable_info(void) { return false; }
 static inline int snp_rmptable_init(void) { return -ENOSYS; }
@@ -677,6 +678,7 @@ static inline void __snp_leak_pages(u64 pfn, unsigned int npages, bool dump_rmp)
 static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
 static inline void kdump_sev_callback(void) { }
 static inline void snp_fixup_e820_tables(void) {}
+static inline void snp_prepare(void) {}
 #endif
 
 #endif
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 0256069..ccec529 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -132,7 +132,7 @@ static unsigned long snp_nr_leaked_pages;
 #undef pr_fmt
 #define pr_fmt(fmt)	"SEV-SNP: " fmt
 
-static __init void mfd_enable(void *arg)
+static void mfd_enable(void *arg)
 {
 	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
 		return;
@@ -140,7 +140,7 @@ static __init void mfd_enable(void *arg)
 	msr_set_bit(MSR_AMD64_SYSCFG, MSR_AMD64_SYSCFG_MFDM_BIT);
 }
 
-static __init void snp_enable(void *arg)
+static void snp_enable(void *arg)
 {
 	u64 val;
 
@@ -503,6 +503,33 @@ static bool __init setup_rmptable(void)
 	return true;
 }
 
+void snp_prepare(void)
+{
+	u64 val;
+
+	/*
+	 * Check if SEV-SNP is already enabled, this can happen in case of
+	 * kexec boot.
+	 */
+	rdmsrq(MSR_AMD64_SYSCFG, val);
+	if (val & MSR_AMD64_SYSCFG_SNP_EN)
+		return;
+
+	clear_rmp();
+
+	cpus_read_lock();
+
+	/*
+	 * MtrrFixDramModEn is not shared between threads on a core,
+	 * therefore it must be set on all CPUs prior to enabling SNP.
+	 */
+	on_each_cpu(mfd_enable, NULL, 1);
+	on_each_cpu(snp_enable, NULL, 1);
+
+	cpus_read_unlock();
+}
+EXPORT_SYMBOL_FOR_MODULES(snp_prepare, "ccp");
+
 /*
  * Do the necessary preparations which are verified by the firmware as
  * described in the SNP_INIT_EX firmware command description in the SNP
@@ -510,8 +537,6 @@ static bool __init setup_rmptable(void)
  */
 int __init snp_rmptable_init(void)
 {
-	u64 val;
-
 	if (WARN_ON_ONCE(!cc_platform_has(CC_ATTR_HOST_SEV_SNP)))
 		return -ENOSYS;
 
@@ -521,22 +546,8 @@ int __init snp_rmptable_init(void)
 	if (!setup_rmptable())
 		return -ENOSYS;
 
-	/*
-	 * Check if SEV-SNP is already enabled, this can happen in case of
-	 * kexec boot.
-	 */
-	rdmsrq(MSR_AMD64_SYSCFG, val);
-	if (val & MSR_AMD64_SYSCFG_SNP_EN)
-		goto skip_enable;
-
-	clear_rmp();
-
-	/* MtrrFixDramModEn must be enabled on all the CPUs prior to enabling SNP. */
-	on_each_cpu(mfd_enable, NULL, 1);
-
-	on_each_cpu(snp_enable, NULL, 1);
+	snp_prepare();
 
-skip_enable:
 	/*
 	 * Setting crash_kexec_post_notifiers to 'true' to ensure that SNP panic
 	 * notifier is invoked to do SNP IOMMU shutdown before kdump.